1. Field of the Invention
This invention relates to a process of optical sizing and to the means for using the process. This invention particularly relates to 100% dimensional control of pieces in a production line. It is applied best but not exclusively to control small size metal pieces whose tolerances are on the order of a micron and the sizes from a few millimeters to centimeters. The invention also lends itself as well to the measurement of absolute sizes and to the comparison of one size in relation to a reference.
2. Background of the Prior Art
A known optical control method resorts to the appearance of Moire figures by the superposition of light fringes projected on the object to be measured and fringes of a mask obtained from a reference piece. Another known optical control method is described in patent application No. CH 8715/77. Here the difference in relation to a reference size is obtained by determining the amount of light going through a mask and coming from the object to be measured, the object being illuminated through a grid.
These methods suffer from the drawbacks that they require the projection of fine fringes of very high contrast and the mask must be very exact.
The control is made on a surface element, or even on the entire surface of the object to be measured. For this reason, the signal-to-noise ratio is slight when the error to be detected is small in relation to the surface element scanned. Moire fringes are generally difficult to interpret quantitatively, and detection of the light that has gone through a mask provides only a "mean" value of the defects present. Further, both methods are sensitive to the surface of the piece to be measured.